Emulsion cleaners are employed in the metal treatment industry to clean and passivate a metal surface. These type of cleaners are typically oil based and form a macroemulsion when mixed with water. This type of cleaner is typically used to remove gross soil contaminants, fines, and cooling lubricants from machined metal surfaces. The cleaned metal surfaces do not become "water break-free" clean in the traditional sense. This type of "cleaner" leaves an oily film on the surface that provides rust protection.
Emulsion cleaners and clean and passivate treatments sometimes can be interchangeable. Emulsion cleaners usually provide longer term passivation and may be followed by a subsequent step of an oil preservative spray where long times in storage are anticipated. Treated parts may need to remain rust free, while exposed in the manufacturing plant, for from several hours up to thirty days. In order to maintain the rust prevention abilities, these type of cleaners are not rinsed. Commercial emulsion cleaners typically comprising a mixture of oil and emulsifiers which are mixed with water to form an oil-in-water emulsion. In a typical commercial emulsion cleaner, a coupling agent or variety of coupling agents are used to produce a stable concentrate. Conventional coupling agents include butyl cellosolve, butyl carbitol or some similar glycol ether to produce a stable concentrate. Currently, glycol ethers are listed as toxic or hazardous under SARA 313 which makes their use in a commercial setting undesirable.
Typical commercial emulsion cleaners employ oil soluble rust inhibitors which are compatible with the oil phase. Such oil soluble rust inhibitors are relatively easy to incorporate into a stable concentrate. In practice, the emulsion baths tend to be metastable and separate to some extent into a oil rich layer and an aqueous layer. Concentration gradients occur with the oil layer being rich in the oil soluble rust inhibitor and the aqueous phase being depleted in rust inhibiting components. When such separation occurs, the metal surfaces being treated are not adequately protected from rusting.